For ease of understanding and explanation, parking meters, and structural elements thereof, will hereafter be used as illustrative of all of the oxygen, humidity and vandalism sensitive devices to which this invention is directed. The use of such illustrative elements in this specification is not intended to be limiting on the scope of the instant invention, but rather should be taken as a convenient short hand method of determining and describing this invention.
Parking meters, vending machines, public telephones and the like, comprised in whole or in part of oxidation sensitive ferrous metals, or other oxidation sensitive materials, are well known to be subject to damage through environmental deterioration because of rusting, crazing, cracking, pitting and the like. All devices that are generally available to the public are routinely subject to abuse by reason of vandalism or accidental collision. It is well known that outdoor devices are often scratched or dented because of malicious mischief or as a result of just plain accidental encounters, for example by reason of an automobile running into a parking meter or a gasoline pump of a toll collection basket, etc. The readily oxidizable ferrous metal parts of a device, even if they are intended for use inside a structure and not out of doors, are still subject to environmental deterioration since the devices are not usually hermetically sealed. In any case, possible damage because of vandalism can always be a problem that needs to be addressed.
The art is replete with means for preventing, or at least reducing, the impact of, such damage by applying coatings made of various compositions at least to exposed ferrous metal members of the outdoor devices. One very common protective method is to galvanize ferrous metal parts, i.e. by applying a zinc based coating thereon followed by conventional galvanizing. Galvanizing certainly assists in preventing or at least retarding corrosive action of the environment and thereby increases the life of ferrous metal parts that have been galvanized. However, galvanizing is not the ultimate protection. It is intended that parking meters be left in place for a very long time, on the order to 50 years. Clearly, their protection must be more than minimal.
It is well known to apply oxidation and scratch resistant polymeric coatings over both the oxidizable ferrous metal and other structural elements of outdoor devices in order to protect them from damage. These polymeric coatings can be applied directly to the metal, e.g. coating directly on oxidizable ferrous metal surfaces, or they can be applied over an intermediate coating layer of some other composition, for example on top of a zinc galvanizing layer. Multiple polymeric layers are also generally known, although these have not been applied to parking meters and the like. In addition to polymeric coatings that can be applied by brushing, spraying or otherwise, it is known to apply suitable coatings over devices or parts thereof by the use of so-called powder application. Both cationic as well as anionic electrocoating application of polymeric coatings, such as specially formulated paint, is a well known method employed in the automobile industry to coat parts of cars that are not readily accessible, such as the inside of rocker panels. Both cationic and anionic electrocoating techniques are generally well known.
Powder coating is carried out by depositing an appropriately formulated powder on the part being coated, applying a d.c. electrostatic charge of opposite polarity to the powder and the substrate, respectively, heating the powder, suitably through the substrate especially if it is a good heat conductor, sufficient to melt the powder and to cause it to flow and spread out to cover the substrate to a film thickness that prevents, or at least substantially reduces, the advent of pinholes or surface cracks and crazing in the resultant coating, and, after the powder has become a substantially continuous coating, cooling the coated substrate and thereby solidifying the coating and adhering it to the substrate. The object here is to provide a coating that is of minimal thickness sufficient to insure substantially complete coverage that will resist environmental attack on the surface portions of the substrate that would otherwise be exposed to the atmosphere, and to resist or at least ameliorate the adverse effects of vandalism or accidental collision. Further, the coating should be of a tough material that tends to prevent penetration by sharp objects such as a knife or a nail. Thus, the coating should have a minimal thickness sufficient to substantially prevent, collision, malicious scratching or atmospheric attack. In general, non-epoxy, meltable polymer coating compositions, such as those set forth in the above identified parent application, are suitable for this use. They are conveniently applied as it powder and converted into a thin protective thermosetting polymer film by the above described process.
Certain applicable prior art is disclosed in the parent application/patent, and such disclosure is incorporated herein by reference. The parent application/patent also discloses very effective coatings for ferrous metal parts that are intended for use in an outdoor environment. These coatings comprise multiple layers including: a hot dipped zinc intermediate layer, covered by an electrostatically applied non-epoxy, organic, electrically insulating thermosetting layer that had been applied by a powder coating method. This improved product has been found to be an excellent preventor of environmental and other damage. However, as with all things, improvements are to be desired.